Basic Terms#

It is important to define some common terms before delving into the technical details.

Physical Layer#

The Physical (PHY) layer is the lowest layer in a communication stack. It is responsible for the transmission of unstructured data through a medium. In a wireless networking stack, the PHY defines the modulation, bit rate, and parts of the frame that are required for successful data reception (for example, the preamble and sync word).

Data Link Layer#

The Data Link Layer (DLL) is built on top of the PHY in a communication stack. It is responsible for reliable data transfer between two devices (for example, addressing, acknowledgement and integrity checks). In IEEE 802 protocols, the DLL is built up from two layers. The lower one is called the Media Access Control (MAC) layer. Because IEEE 802.15.4 does not have the upper DLL, the MAC layer is interchangeable with DLL.

Personal Area Network#

A Personal Area Network (PAN) is a logical group of devices that can communicate with each other. Protocols built on IEEE 802.15.4 usually communicate inside a PAN.

PAN Coordinator#

The PAN coordinator can perform special services in some protocols (for example, allocating short addresses).

Intra-PAN Message#

An intra-PAN message is one where the source and destination device are in the same PAN.

Inter-PAN Message#

An inter-PAN message is one where the source and destination device are in different PANs.

Long Address#

A long address is a globally unique 64-bit address (EUI64). Each Silicon Labs Wireless Gecko is assigned an EUI64 address at the factory. This is standardized across most IEEE 802 protocols (for example, IPv6 uses the same EUI64 as the MAC address).

Short Address#

A short address is a 16-bit address that is only unique in a PAN. Because IEEE 802.15.4 has a fairly short frame, using long addresses would consume a lot of the frame. Therefore, devices can use short addresses if they also know the PAN ID. 0xFFFE is a reserved special address, which means the device is in the PAN, but does not have a source address and it should use its long address to communicate.

PAN ID#

A PAN ID is a 16-bit long address that identifies a PAN. There is no standardized way to allocate PAN IDs so the application should make sure to use a PAN ID that is not used in the same network.

Broadcast Address#

A broadcast address is special address that should be received by any device. The 0xFFFF short address is the broadcast short address. The 0xFFFF PAN ID is the broadcast PAN ID.

CSMA/CA#

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is a "listen-before-talk" protocol: To avoid collisions, the radio listens to a channel before transmission. If the channel is "free" (that is, nothing was received), the device can transmit. If the channel is "busy" (that is, something was received), the device waits before trying again. After a certain number of retries, the transmit will fail and an error will be reported to the application.

Message Integrity Check#

Message Integrity Check (MIC) is used for data authentication: Only the real sender can calculate the MIC of a frame.